Difference Between Bursa and Synovial Fluid

The key difference between bursa and synovial fluid is that bursa is a tiny fluid-filled sac found around a joint while synovial fluid is the viscous, slippery fluid that fills cavities of synovial joints.

Synovial joints facilitate smooth movements between bones. Synovial cavity is present in a synovial joint, and it is filled with synovial fluid. Synovial fluid facilitates lubrication, nutrient distribution and shock absorption. Bursa is an additional structure located near the synovial joint. It is a tiny fluid-filled sac involved in reducing friction between the bones of a joint. Therefore, both synovial fluid and bursa act as shock absorbers in joints.

CONTENTS

1. Overview and Key Difference
2. What is Bursa
3. What is Synovial Fluid
4. Similarities Between Bursa and Synovial Fluid
5. Side by Side Comparison – Bursa vs Synovial Fluid in Tabular Form
6. Summary

What is Bursa?

Bursae are tiny fluid-filled slippery sacs found around a joint. They are surrounded by a synovial membrane and filled with synovial fluid. When a muscle, tendon, skin and ligament glides over bones during joint movement, bursa provides a thin cushion and reduces the friction. Therefore, bursae mainly cushion the bones in order to reduce friction. In the human body, there are about 150 bursae – each one is like a miniature water balloon. Most of them are present at birth. However, some may form later in areas that are frequently subjected to friction.

Adventitious, subcutaneous, synovial and submuscular bursae are the four types of bursae found in our body. Adventitious bursae are found in places that are exposed to friction. Subcutaneous bursae are present just under the skin. Synovial bursae are present in the synovial joints. Submuscular bursae are found under the muscle.

What is Synovial Fluid?

Synovial joint is the most common type of joint present in humans. It joins bones with a fibrous joint capsule. There is a fluid-filled joint cavity in the synovial joint. This synovial cavity is filled with synovial fluid. Synovial fluid is a viscous fluid with egg white-like consistency.

Synovial membrane secretes the synovial fluid, and it is a component of transcellular fluid component of extracellular fluid. This fluid contains proteins derived from the blood plasma and proteins produced by cells within the joint tissues. Moreover, it contains hyaluronan, lubricin and interstitial fluid. The key functions of synovial fluid are lubrication, nutrient distribution and shock absorption.

What are the Similarities Between Bursa and Synovial Fluid?

• Both bursa and synovial fluid are shock absorbers.
• Bursae are filled with synovial fluids.
• They help reduce friction between bones in a joint.

What is the Difference Between Bursa and Synovial Fluid?

Bursae are tiny fluid-filled sacs which facilitate gliding movements of tendons, ligaments, muscles, and skin over bones during joint movement while synovial fluid is the fluid that fills the synovial cavity of the synovial joint. So, this is the key difference between bursa and synovial fluid. Besides, bursae are found around tendons, ligaments, muscles, and skin moving across a bony surface while synovial fluid is located within the synovial cavity of a synovial joint.

Moreover, structurally, bursae are small fluid-filled sacs while synovial fluid is a viscous, slippery, lubricating fluid. Hence, this is the structural difference between bursa and synovial fluid. Also, functionally, bursae provide a cushion between bones and tendons and/or muscles around a joint and reduce the friction between bones when moving while synovial fluid help in lubrication, nutrient distribution and shock absorption.

Below infographic summarizes the difference between bursa and synovial fluid.

Summary – Bursa vs Synovial Fluid

Bursae are tiny fluid-filled sacs that are found around joints. Synovial fluid is a viscous slippery lubricating fluid that fills that synovial cavity of synovial joint. Thus, this is the key difference between bursa and synovial fluid. Bursa is lined by the synovial membrane, and it is filled with the synovial fluid. Synovial fluid contains proteins, hyaluronan, lubricin and interstitial fluid. Both bursa and synovial fluid reduce friction between bones of the joint. They are also shock absorbers.

Reference:

1. “9.4 Synovial Joints”. Opentextbc.Ca, 2020, Available here.
2. “Synovial Fluid”. En.Wikipedia.Org, 2020, Available here.

Image Courtesy:

1. “908 Bursa” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Joint” By Madhero88 – Own work (CC BY-SA 3.0) via Commons Wikimedia